Light Control Devices Implemented With Diffusers Having Controllable Diffusion Characteristics

ABSTRACT

Light control devices implemented with diffusers exhibiting controllable diffusion characteristics provide anisotropic luminous intensity distributions and glare control at high viewing angles while maintaining high luminaire efficiency or daylight utilization.

RELATED APPLICATIONS

This is a continuation filed under 35 U.S.C. §120 of U.S. patentapplication Ser. No. 11/601,452, filed Nov. 17, 2006 which is acontinuation-in-part of U.S. patent application Ser. No. 09/907,536, nowU.S. Pat. No. 7,660,039, filed Jul. 16, 2001, which claims benefit ofU.S. Provisional Patent Application Nos. 60/294,423 and 60/218,224,filed May 29, 2001 and Jul. 14, 2000, respectively, all of which arehereby incorporated within by reference.

TECHNICAL FIELD

The present invention disclosure pertains to the fabrication of kinoformdiffusers having controllable diffusion characteristics that includepredetermined and desirable physical properties relating to diffusion ofachromatic illumination. More particularly, light control devices thatare used for artificial illumination and daylighting, includingresidential, commercial, industrial, and roadway lighting applications.The light control devices are implemented with kinoform diffusers of atype exhibiting controllable diffusion characteristics to provideanisotropic luminous intensity distributions and glare control at highviewing angles while maintaining good luminaire efficiency or daylightutilization.

BACKGROUND INFORMATION

Diffusers scatter incident electromagnetic radiation (e.g., visiblelight, infrared, and ultraviolet radiation) by means of diffusetransmission or reflectance. Considered as components of imaging andnon-imaging optical systems design, an ideal diffuser would exhibit thefollowing physical characteristics:

1. Scattering within a specified beam distribution. When a ray ofcollimated (but not necessarily coherent) light is incident upon adiffuser at an angle θ(i), the transmitted or reflected light would berandomly scattered through a range of angles between θ(t1) and θ(t2) fortransmitted light or θ(r1) and θ(r2) for reflected light. These anglesare shown in FIG. 1 and represent the limits of the transmitted orreflected beam distribution pattern. FIG. 1 is a schematic illustrationof the scattering of incident beams of collimated light by prior arttransmissive and reflective diffusers. Collimated light beam 10 isperpendicular to the surface of a conventional transmissive diffuser 12and is scattered into a beam distribution 14. The beam distributionmaximum is perpendicular to the surface of diffuser 12. A collimatedlight beam 16 is incident to a surface normal n of conventional diffuser12 at an angle θ(i) and is scattered into a beam distribution 18. Thebeam distribution maximum (the “central axis” of the beam distribution)is inclined at an angle θ(t) relative to surface normal n of diffuser 12and is equal to angle θ(i).

A collimated light beam 20 is perpendicular to the surface of aconventional reflective diffuser 22 and is scattered into a beamdistribution 24. The beam distribution maximum is perpendicular to thesurface of diffuser 22. A collimated light beam 26 is incident to asurface normal n of conventional diffuser 22 at an angle θ(i) and isscattered into a beam distribution 28. The beam distribution maximum isinclined at an angle θ(r) relative to surface normal n of diffuser 22and is equal to angle θ(i).

2. No scattering outside of the specified beam distribution. No incidentlight would be scattered outside of the specified beam distributionranges.

3. Uniform beam distribution. The incident light would be uniformlyscattered within the specified beam distribution.

4. No backscatter. If the diffuser transmits rather than reflectsincident light, none of the incident light would be reflected by thediffuser.

5. No absorption. None of the incident light would be absorbed by atransmissive diffuser.

6. Complete diffusion. It would not be possible to see an image of thelight source or “hot spot” when looking at the light source through atransmissive diffuser. The diffuser would appear to have a constantluminance (“photometric brightness”) distribution across its surface.

7. Wavelength independence. The scattering properties of the diffuserwould be independent of the wavelength of the incident light over aspecified range of wavelengths.

For the purposes of optical systems design flexibility, two additionalphysical characteristics would sometimes be desirable:

8. Anisotropic beam distribution. The beam distribution of the diffuserwould be anisotropic about the central beam axis, includingdistributions that are elliptical or linear, as shown in FIG. 2. FIG. 2is a schematic illustration of the cross-sections of the scattered lightbeam distributions from a prior art isotropic (circular) diffuser 30,elliptical anisotropic diffuser 32, and substantially linear anisotropicdiffuser 34.

9. Off-axis beam distribution. The central axis of the beam distributionwould be at a transmitted angle, θ(t) or θ(t′), as shown in FIGS. 3A and3B, respectively, that is not equal to the incidence angle, θ(i), asmight be predicted by Snell's Law. FIGS. 3A and 38 are schematicillustrations of off-axis beam distributions for transmissive kinoformdiffusers designed in accordance with the invention with their surfacerelief patterns facing, respectively, away from and toward the directionof incident light. A collimated beam 36 is incident to surfaces withnormal n of transmissive kinoform diffusers 38 at an angle θ(i) and isscattered into beam distributions 40 and 40′. The beam distributionmaxima are at angles θ(t) and θ(t′) to surface normal n of kinoformdiffusers 36. The beam distribution also varies depending on the patternorientation. In particular, annular distributions (FIGS. 8C and 8D) areachievable with the pattern facing the light source. Similarly, thecentral axis of the beam distribution would be at a reflected angle,θ(r), as shown in FIG. 4, that is not equal to the incidence angle,θ(i), as might be predicted by the law of reflection from specularsurfaces. FIG. 4 is a schematic illustration of an off-axis beamdistribution for a reflective kinoform diffuser designed in accordancewith the invention. A collimated beam 42 is incident to a surface withnormal n of a reflective kinoform diffuser 44 at an angle θ(i) and isscattered into a beam distribution 46. The beam distribution maximum isat an angle θ(r) to surface normal n of kinoform diffuser 44, whereangle θ(r) is generally not equal to angle θ(i).

Kinoform diffusers may exhibit certain physical characteristics thatapproach those of an ideal diffuser.

Lesem, L. B., Hirsch, P. M., and Jordan, Jr., J. A., “The Kinoform: ANew Wavefront Reconstruction Device,” IBM J. Research and Development,13: 150-55 (1969) introduced a “kinoform,” describing it as acomputer-generated “wavefront reconstruction device” that, similar to ahologram, provides the display of a three dimensional image. Unlike ahologram, however, the kinoform yields a single diffraction order inwhich all of the incident light is used to reconstruct the image. Akinoform operates only on the phase of an incident wave, because it isassumed that only the phase information in a scattered wavefront isrequired for the construction of an image of the scattering object. Theamplitude of the wavefront in the kinoform plane is assumed to beconstant.

Caulfield, H. J., “Kinoform Diffusers,” SPIE Vol. 25, Developments inHolography, 111-13 (1971) stated that a kinoform of a “scatteringobject” constituting a conventional diffuser, such as ground glass,could be generated by photographic techniques, thereby producing a“kinoform diffuser.” U.S. Pat. No. 3,619,021 of Biedermann et al.describes a technique for constructing a kinoform diffuser, which iscalled in their patent simply a “diffusing layer.”

FIG. 5 shows a basic prior art optical setup used to record kinoformdiffusers as taught by Caulfield. (As will be appreciated by thoseskilled in the holographic arts, many variations in the optical setupare possible.) A laser 48 produces a beam of coherent light 50 that isexpanded by lenses 52 and 54 to fully and evenly illuminate a diffuser60 with a coherent planar wavefront propagating through an opaque mask56 having an aperture 58. A photosensitive recording plate 62 is locateda distance, d, behind diffuser 60. (Suitable photosensitive materialsinclude positive and negative photoresist emulsions, silver halidefilms, dichromated gelatin, and various photopolymers.)

The light scattered by diffuser 60 produces on a surface ofphotosensitive recording plate 62 a random laser speckle pattern that isrecorded photographically. Photosensitive plate 62 is developed inaccordance with known processing techniques to produce a transparentsubstrate with a surface relief pattern whose spatially distributedheight distribution is proportional to the spatially distributedintensity of the recorded laser speckle pattern, which is shown in FIG.6. This is the transmissive kinoform diffuser. A reflective kinoformdiffuser can be fabricated by, for example, applying an evaporated metalfilm to the surface of the transmissive diffuser. Alternatively, thesurface relief pattern can be transferred using known replicationtechniques such as embossing or molding to an opaque metallic or plasticsubstrate.

When the transmissive kinoform diffuser is illuminated by a coherentplanar wavefront, the length of the optical path through the diffuser atany point is determined by the height of the surface relief pattern atthat point. Because the phase retardation of the wavefront propagatingthrough the diffuser is dependent on the optical path length, the planarwavefront is randomly scattered according to the surface relief patternof the kinoform diffuser. In theory, the kinoform diffuser reconstructsthe laser speckle pattern generated by ground glass diffuser 60.

The same principle applies to reflective kinoform diffusers, except thatthe differences in optical path length and subsequent phase retardationoccur in free air or other optically transparent medium immediatelyabove the diffuser surface.

The Caulfield publication and certain other references noted thefollowing observations:

1. The beam distribution of the kinoform diffuser is dependent on thedistance, d, between diffuser 60 and recording plate 62. Increasing ddecreases the range of angles θ(t1) to θ(t2), between which substantialdiffusion occurs.

2. The angular intensity distribution of scattering is highlynon-uniform, as shown in FIG. 7. Dainty, J. C., “The Statistics ofSpeckle Patterns,” Progress in Optics XIV, E. Wolf, (ed.), New York,N.Y.: North-Holland, 3-46 (1976) sets forth the following expressiondemonstrating that the expected beam distribution can be characterizedby a negative exponential function:

I _(θ) =A*exp(−B*I _(θ)),  (1)

Where I_(θ) is the expected intensity at angle θ from the axis of theincident ray, I₀ is the incident ray intensity, and A and B are positiveconstants.

3. Tilting diffuser 60 or recording plate 62 about an axis perpendicularto the laser beam axis produces kinoform diffusers with anisotropic beamdistributions that are approximately elliptical, as shown in FIG. 2.Wadle S., Wuest, D., Cantalupo, J., et al., “Holographic Diffusers,”Optical Engineering, 33(1):213-18 (January 1994) stated that theequivalent effect can be achieved by using a rectangular aperture inopaque mask 56, and U.S. Pat. No. 3,698,810 of Bestenreiner et al.described the use of one narrow slit aperture or multiple narrow slitapertures to produce substantially linear beam distributions.

4. Gray, P. F., “A Method for Forming Optical Diffusers of Simple KnownStatistical Properties,” Optica Acta 25(8):765-775, noted that theexpected beam distribution of kinoform diffusers produced using Nmultiple exposures with uncorrelated laser speckle patterns can becharacterized by the function:

P=(I ^(N-1)/(N−1)!)*exp(−N*I).  (2)

This function tends towards a substantially Gaussian function as thenumber of exposures N increases, as shown in FIG. 9.

The Lesem et al. publication noted that while there is only one image(i.e., diffraction order) formed in the laser speckle patternreconstruction, there might be a “zero-order beam” componentrepresenting a portion of the undiffracted planar wavefront. Visually,the light source illuminating a kinoform diffuser can be seen when it isviewed directly through the diffuser, indicating incomplete diffusion.This blurred image can theoretically be eliminated by perfect phasematching within the kinoform.

The Caulfield publication demonstrated that elimination of thezero-order beam (and hence complete diffusion) could be achievedexperimentally by adjusting the exposure of the photosensitive platesuch that the transmitted beam was not visible through the kinoformdiffuser. However, this applied only to monochromatic light sources.Kowalczyk, M., “Spectral and Imaging Properties of Uniform Diffusers,”J. Optical Society of America, A1(2):192-200 (February 1984) performed atheoretical analysis of kinoform diffusers and demonstrated that phasematching is wavelength-dependent. That is, the zero-order beam componentcan (in theory) be eliminated for monochromatic illumination only. Whenilluminated by an achromatic (or “white”) light source, these diffusersmay exhibit significant spectral dispersion that appears as color bandssurrounding the light source image that will be visible through thediffuser.

Although they were originally developed for holographic recording andreconstruction purposes, kinoform diffusers also effectively scatterquasi-monochromatic and polychromatic light, such as that produced bylight-emitting diodes, and substantially achromatic light, such asdaylight and artificial light produced by incandescent, fluorescent, andhigh intensity discharge lamps. Examples of such uses are given in U.S.Pat. No. 4,602,843 of Glaser-Inbari, U.S. Pat. No. 5,473,516 of VanOrder et al., U.S. Pat. No. 5,534,386 of Petersen et al., and U.S. Pat.No. 5,701,015 of Lungershausen et al.

Kinoform diffusers for achromatic light applications of a type known as“surface-relief holographic diffusers” are commercially available. Forexample, Physical Optics Corporation (Torrance, Calif.) manufactures aseries of products called “Light Shaping Diffusers.” These diffusers mayexhibit substantial elimination of the zero-order beam with achromaticlight sources. That is, they are wavelength-independent across thevisible spectrum. As taught by Gray, this can be achieved by exposingthe photosensitive plate to a multiplicity of uncorrelated laser specklepatterns.

A disadvantage of surface-relief holographic diffusers is that theirsurface relief height distributions are (within the limits of knownphotographic recording techniques and replication technologies) directlyproportional to the intensity distributions of the recorded laserspeckle patterns. As shown theoretically by Dainty and experimentally byGray, their beam distributions are necessarily characterized bysubstantially Gaussian functions.

A properly designed kinoform diffuser may, therefore, exhibit thefollowing generally desirable physical characteristics:

1. Scattering within a specified beam distribution. The range of angleswithin which substantial scattering occurs may be controlled by varyingthe distance, d, between diffuser 60 and recording plate 62 (FIG. 5).

2. Minimal backscatter. Backscatter may occur substantially only byreflection from the surfaces of a transmissive kinoform diffuser and maybe substantially eliminated by the application of suitableantireflection coatings to said surfaces.

3. Minimal absorption. Incident light is absorbed substantially onlywithin the transparent substrate of a transmissive kinoform diffuser.

4. Anisotropic beam distribution. The eccentricity of an elliptical beamdistribution may be determined by the ratio of length to width ofrectangular aperture 58 in opaque mask 56 (FIG. 5).

5. Complete diffusion. When it is purposefully designed to providesubstantial elimination of the zero-order beam with achromatic lightsources, the kinoform diffuser exhibits substantially complete diffusionof the incident light and freedom from spectral dispersion.

Unfortunately, a kinoform diffuser may also exhibit the followinggenerally undesirable physical characteristics:

1. Significant scattering outside of the specified beam distribution.Because the expected beam distribution is characterized by a negativeexponential or substantially Gaussian function, prior art techniques donot limit the scattering of the incident light to be fully within aspecified range of angles.

2. Non-uniform beam distribution. A kinoform diffuser constructed usingprior art techniques exhibits within the specified range of angles anexpected beam distribution that is necessarily of a nonuniform negativeexponential or substantially Gaussian shape. Kurtz, C. N.,“Transmittance Characteristics of Surface Diffusers and the Design ofNearly Band-Limited Binary Diffusers,” J. Optical Society of America62(8):982-989 (August 1972) and others show that kinoform diffusers withuniform beam distributions are theoretically possible, but provide noguidance in how they might be physically realized.

One preferred use of the kinoform diffusers described herein is theirimplementation in luminaires. Luminaires (also known as “lightfixtures”) intended for general illumination applications are designedwith the objectives of providing specific luminous intensitydistributions while minimizing glare at high viewing angles and lightlosses within the luminaire housing. Designing luminaires to meet theseobjectives can be challenging, particularly when there are restraints onthe physical size of the luminaire.

The luminous intensity distribution is determined by the placement andoptical properties of lamps and light control components such asreflectors, refractors, diffusers, and shields (including louvers andbaffles). There are many applications in which anisotropic luminousintensity distributions are used. For example, indirect fluorescentluminaires intended for office lighting typically require so-called“batwing” distributions (FIGS. 13A-13C) that provide even illuminationof the ceiling (Illuminating Engineering Society of North America(IESNA) [2000]). The light control components are designed to redirector absorb the light emitted by the lamps to achieve the desired luminousintensity distribution.

A disadvantage of light control components is that they absorb light andthereby reduce the luminaire efficiency. American National StandardsInstitute (ANSI)/IESNA [1996] defines luminaire efficiency as: “Theratio of the luminous flux (lumens) emitted by a luminaire to thatemitted by the lamp or lamps used therein.”) Tradeoffs are, therefore,made by a designer between the need to achieve specific luminousintensity distributions and minimum acceptable luminaire efficiencies.

Another aspect of luminaire design is the minimization of glare at highviewing angles (FIG. 14). (ANSI/IESNA [1996] defines glare as: “Thesensation produced by luminaires within the visual field of view thatare sufficiently greater than the luminance to which the eyes areadapted to cause annoyance, discomfort, or loss in visual performance orvisibility.”) For example, ceiling-mounted office luminaires 70 shoulddirect most of their emitted light downward to the work plane 72. Ifthey emit too much light horizontally, they will appear distractinglybright when viewed directly. Worse, their veiling reflections fromcomputer monitor screens may reduce office productivity.

Glare can be minimized by blocking the emitted light with shields.However, this increases the light losses within the luminaire housingand so reduces the luminaire efficiency. These losses can be reduced byusing reflectors or refractors instead of shields, but this approach maylimit a designer's ability to achieve specific luminous intensitydistributions.

Glare can also be minimized using glass or plastic diffusers. These arepreferable to shields in that the light is emitted from a larger surfacearea (that is, the diffuser instead of the lamp) and so reduces themaximum luminance of the luminaire (IESNA [2000]). However, thesediffusers typically absorb as much as one-half of the incident light,thereby reducing the luminaire efficiency. They also emit light in alldirections within the hemisphere above their surfaces, thereby furtherlimiting a designer's ability to achieve specific luminous intensitydistributions.

In the related field of daylighting, light control devices such asshields and diffusers are often used to control sunlight entering abuilding through windows and skylights. Diffusers such as frosted glassand plastic panels are used to limit glare and reduce dark shadows,while light control devices such as louvers, mirrors, and motor-drivenheliostats may be used to control and redirect sunlight through windowsand skylights. As with luminaires, however, diffusers absorb aconsiderable portion of the incident sunlight and offer little controlover the distribution of the diffused light.

There have been numerous prior attempts to control the luminousintensity distribution of luminaires and light sources using diffractivevolume holograms and commercial holographic diffusers (which havesimilar optical performance characteristics to those of kinoformdiffusers).

Davis (U.S. Pat. Nos. 4,536,833, 4,704,666, 4,713,738, and 4,722,037)described the use of multi-layered holograms as light control elements.Unlike kinoform diffusers, multi-layer holograms do not providecontrollable diffusion or exhibit off-axis transmission properties,which are features of the kinoform diffusers described herein. They alsofunction usefully as light control elements only for predeterminedwavelengths. When used with achromatic light sources such as arecommonly used for general illumination applications, multi-layerholograms exhibit unacceptable spectral dispersion effects (visible ascolor “fringes”) and high absorption characteristics.

Jannson et al. (U.S. Pat. No. 5,365,354) described various applicationsof volume holographic diffusers that involve luminaires designed forgeneral illumination applications. However, these applications relysolely on the well-known anisotropic diffusion capabilities ofcommercial holographic diffusers.

Petersen et al. (U.S. Pat. No. 5,534,386) similarly described variousapplications of surface-relief holographic diffusers that involveluminaires designed for general illumination applications. Theseapplications also rely solely on the anisotropic diffusion capabilitiesof holographic diffusers.

Van Order et al. (U.S. Pat. Nos. 5,473,516 and 5,582,474) described avehicle light assembly that utilizes a holographic diffuser withcircular or elliptical luminous intensity distribution characteristics.This vehicle light assembly requires that the light emitted from thelamp be substantially collimated by a reflector to effectivelyilluminate the holographic diffuser.

Fox (U.S. Pat. No. 5,630,661) described a metal arc flashlight thatoptionally includes a holographic diffuser. This flashlight alsorequires that the light emitted from the lamp be substantiallycollimated by a reflector to effectively illuminate the holographicdiffuser.

Smith (U.S. Pat. No. 5,669,693) described an automotive tail lampassembly that utilizes a holographic element to diffract light emittedby a light emitting diode assembly in a preferred direction. This taillamp assembly relies on the quasi-monochromatic emission oflight-emitting diodes, and is not suitable for use with achromatic lightsources such as incandescent or high-intensity discharge lamps.

Lungershausen et al. (U.S. Pat. No. 5,701,015) described an infraredillumination system for digital cameras that utilizes a holographicdiffuser to homogenize the light emitted by infrared laser diodes. Thisillumination system requires that the emitted light be substantiallycollimated to effectively illuminate the holographic diffuser.

Hewitt (U.S. Pat. No. 6,062,710) described various luminaire designsthat utilize holographic diffusers to reduce glare. Unlike the presentinvention, these designs are predicated on the use of imaging opticalelements to substantially collimate the light that illuminates theholographic diffuser.

Shie, et al. (WIPO International Publication Number WO 00/11498)described various applications of holographic diffusers that involveluminaires designed for general illumination applications. Theseapplications are based on the process of molding surface-reliefdiffusers directly onto the surface of transparent optical elementsusing injection molding or casting. The described applications relysolely on the anisotropic diffusion capabilities of holographicdiffusers and some mechanically produced diffusion patterns.

Shie et al. (WIPO International Publication Number WO 00/11522) furtherdescribed various applications of holographic diffusers that involveluminaires designed for general illumination applications. Theseapplications are based on the process of embossing surface-reliefdiffusers directly onto the surface of transparent optical elementsusing a sol gel process. The described applications similarly relysolely on the anisotropic diffusion capabilities of holographicdiffusers and some mechanically produced diffusion patterns.

Saito (Japanese Patent No. 6-76618) described a lighting systemcomprising a light source and a holographic element acting as a dichroicmirror to reflect light of substantially one wavelength. The lightingsystem does not function properly when used with achromatic lightsources.

Regarding daylight control, large plastic diffraction gratings have beenused to redirect sunlight entering building through skylights andwindows. The disadvantage of using such gratings is that they exhibitsevere spectral dispersion. This is evident both as color fringessurrounding objects viewed through the gratings and as the separation ofsunlight into a diffuse color spectrum that is visible on the walls,floor, and ceiling of the room.

Multi-layer volume holograms have been used as a replacement fordiffraction gratings in an attempt to limit the effects of spectraldispersion. However, these light control devices suffer from lowtransmittance and consequent poor daylight utilization.

SUMMARY OF THE DISCLOSURE

This disclosure enables construction of kinoform diffusers that exhibitcontrollable diffusion characteristics with off-axis transmittance andreflectance properties, elimination of zero-order beam, and freedom fromspectral dispersion under achromatic illumination. Kinoform diffusersmade in accordance with the disclosure embody surface relief patternsthat produce specific beam distributions. These patterns are embodied inphysical kinoform diffusers using known photographic techniques andreplication technologies. The disclosed embodiments enable physicallyrealizable specific beam distributions other than beam distributionscharacterized by a negative exponential or substantially Gaussianfunction.

Laboratory experiments performed by the applicants have revealed atleast four classes of kinoform diffusers with desirable non-Gaussianbeam distributions. These beam distributions are shown in FIGS. 8A, 8B,8C, and 8D. A first class is characterized by a beam distribution thatis substantially contained within a controllable range of angles andthat has a substantially uniform distribution within that range (FIG.8A). A second class is an elliptical or linear (anisotropic) variant ofthe first class (FIG. 8B). A third class is also characterized by a beamdistribution that is substantially contained within a controllable rangeof angles but has an annular beam distribution that is desirable forarchitectural lighting applications utilizing compact light sources suchas incandescent or high intensity discharge lamps (FIG. 8C). A fourthclass is an elliptical or linear (anisotropic) variant of the thirdclass. It is desirable for architectural lighting applicationsimplemented with linear light sources such as linear fluorescent lampsor linear arrays of light-emitting diodes (FIG. 8D).

Laboratory experiments performed by the applicants have revealed thatthese four classes of diffusers can be produced by careful preparation,exposure, and development of the photosensitive plates to yield complexsurface relief patterns whose height distributions are not directlyproportional to the intensity distributions of the recorded laserspeckle patterns. Examples of these surface relief patterns are shown inFIGS. 10, 11, and 12.

The disclosed embodiments effect an off-axis beam distribution from atransmissive kinoform diffuser, as shown in FIGS. 3 and 8E. This isaccomplished apparently by a combination of multiple internal andexternal reflections of the transmitted light, as well as near-fieldinterference effects caused by the microscopic surface relief patternfeatures.

The disclosed embodiments further effect an off-axis beam distributionfrom a reflective kinoform diffuser, as shown in FIGS. 4 and 8F, inwhich the diffuser behaves as a diffusing retroreflector for some rangeof incidence angles. This is accomplished apparently by multipleexternal reflections of the incident light and near-field interferenceeffects caused by the microscopic surface relief pattern features.

Disclosed embodiments can be implemented as a kinoform diffuser thatexhibits a controlled color cast when viewed under conditions ofachromatic illumination. This can be achieved by superimposing a weakholographic diffraction grating onto the kinoform diffuser recording.Varying the parameters of the diffraction grating allows thechromaticity and saturation of the color cast to be controlled.

Disclosed embodiments can be implemented as a kinoform diffuser thatincorporates a holographic watermark for anti-counterfeiting purposes.This can be achieved by superimposing a weak holographic image onto thekinoform diffuser recording. Because it is spatially distributedthroughout the kinoform diffuser, the holographic image is invisibleunder incoherent illumination. It can, however, be observed at specificangles under coherent illumination. Moreover, a weak holographic imageensures that it does not substantially affect the diffuser beamdistribution.

Kinoform diffusers can be used as light control components forartificial illumination and daylighting applications. Kinoform diffusersoffer the novel optical properties of anisotropic diffusion withcontrollable distribution characteristics and off-axis transmittance. Incommon with some holographic diffusers, kinoform diffusers also offernegligible zero-order beam transmission, minimal light loss, and lowbackscatter over a range of incidence angles. These properties enablethe design and manufacture of luminaires that feature anisotropicluminous intensity distributions with minimal glare and high luminaireefficiencies, and of skylights and windows that feature low light lossesand controllable distribution of diffused sunlight.

As described in detail below, the optical properties of kinoformdiffusers are produced by a surface relief pattern on one or bothsurfaces of a transparent or opaque substrate. The diffusers may betransmissive or reflective.

The surface relief pattern of a typical kinoform diffuser is presentedas a scanning electron microscope (SEM) image in FIG. 10. This diffuserproduces a circular (that is, isotropic) diffusion pattern (FIG. 2,leftmost diagram). The surface relief pattern of another typicalkinoform diffuser is presented as a SEM image in FIG. 11. This diffuserproduces a linear (that is, anisotropic) diffusion pattern (FIG. 2,rightmost diagram). Both of these diffusers are transmissive, andcoating their surface relief patterns with an evaporated metal filmproduces reflective diffusers.

When incident light 36 illuminates a transmissive kinoform diffuserwhose surface relief pattern 38 faces away from the direction of theincident light 36

(FIG. 3A), the diffused transmitted light 40 is preferentially directedtowards the surface normal n such that θpeak(t)<θ(i). When the surfacerelief pattern 38 faces towards the direction of the incident light 36(FIG. 3B), the diffused transmitted light 40′ is preferentially directedaway from the surface normal n such that θpeak(t′)>θ(i). This off-axistransmittance does not occur with conventional diffusers.

It should further be noted that when incident light 42 illuminates areflective kinoform diffuser 44 (FIG. 4) at an oblique angle θ(i), thediffused reflected light 46 is preferentially directed towards theincident light source such that θpeak(r)≠θ(i). The retroreflectivebehavior contradicts the law of reflection for specular surfaces [IESNA2000] and does not occur with conventional diffusers.

Kinoform diffusers with elliptical and linear diffusion patterns can beconceptually formed by stretching the surface relief pattern shown inFIG. 10 in a given direction. The roughly circular features shown inFIG. 10 become progressively elliptical; the linear features shown inFIG. 11 are elliptical with an eccentricity of approximately 0.0025.

Linear kinoform diffusers have, therefore, a “plane of diffusion” inwhich an incident beam of collimated light is diffused into a fan-shapeddistribution. This plane is perpendicular to the direction of the linearsurface relief pattern features (FIG. 11). Elliptical kinoform diffusershave a similar plane that is perpendicular to the common major axis ofthe elliptical surface relief pattern features. A linear or anelliptical kinoform diffuser may, therefore, be “oriented” such that itsplane of diffusion is aligned in a particular direction with respect tothe major axis of a linear light source.

The luminaire designs described herein are dependent on the opticalproperties of kinoform diffusers and some holographic diffusers. Ingeneral, such luminaire designs cannot be achieved entirely withconventional light control components such as reflectors, refractors,diffusers, and shields. In particular, they cannot be achieved entirelywith conventional glass or plastic diffusers.

In a first preferred embodiment (FIG. 15), a kinoform diffuser ispositioned below and oriented perpendicular to the major axis of alinear light source such that it both diffuses the emitted light in aplane perpendicular to the light source axis and preferentiallyredirects it downwards towards the work plane. The luminaire has lowluminance at high viewing angles in the vertical plane perpendicular tothe light source axis and thereby minimizes glare.

In a second preferred embodiment (FIG. 16), a circular or an ellipticaldistribution kinoform diffuser is positioned below a point light source(such as a compact incandescent or high-intensity discharge arc lamp)such that it both diffuses the emitted light and preferentiallyredirects it downwards towards the work plane. The luminaire has lowluminance at high viewing angles.

In a third preferred embodiment (FIG. 17), a kinoform diffuser ispositioned below and oriented parallel to the major axis of a linearlight source such that it both diffuses the emitted light in a planeparallel to the light source axis and preferentially redirects itdownwards towards the work plane. The luminaire has low luminance athigh viewing angles in the plane parallel to the light source axis.

In a fourth preferred embodiment (FIG. 18), a linear or an ellipticaldistribution kinoform diffuser is positioned below a point light sourcesuch that it diffuses the emitted light in a vertical plane andpreferentially redirects it downwards towards the work plane. Theluminaire has low luminance at high viewing angles in the planeperpendicular to the plane of diffusion.

In a fifth preferred embodiment (FIG. 19), a series of wedge-shapedlinear distribution kinoform diffusers are positioned below a pointlight source and arranged such that each diffuser is oriented radiallywith respect to said light source. The diffusers both diffuse theemitted light in a vertical plane tangent to nadir and preferentiallyredirect it downwards towards the work plane. The luminaire has lowluminance at high viewing angles.

In a sixth preferred embodiment (FIG. 20), a kinoform diffuser with atransparent central region is positioned below and orientedperpendicular to the major axis of a linear light source such that itboth diffuses the emitted light in a plane perpendicular to the lightsource axis and preferentially redirects it downwards towards the workplane. The luminaire has low luminance at high viewing angles in thevertical plane perpendicular to the light source axis, while thetransparent central region in combination with the diffuser provides alinear batwing luminous intensity distribution.

In a seventh preferred embodiment (FIG. 21), a circular distributionkinoform diffuser with a transparent central region is positioned belowa point light source such that it both diffuses the emitted light andpreferentially redirects it downwards towards the work plane. Theluminaire has low luminance at high viewing angles, while thetransparent central region in combination with the diffuser provides acircular batwing luminous intensity distribution.

In an eighth preferred embodiment (FIG. 23A), an inwardly folded lineardistribution kinoform is positioned below and oriented parallel to themajor axis of a linear light source such that it both diffuses theemitted light in a plane parallel to the light source axis andpreferentially redirects it downwards towards the work plane. Theluminaire has low luminance at high viewing angles in all verticalplanes.

In a ninth preferred embodiment (FIG. 25A), an outwardly folded lineardistribution kinoform is positioned below and oriented parallel to themajor axis of a linear light source such that it both diffuses theemitted light in a plane parallel to the light source axis andpreferentially redirects it downwards towards the work plane. Theluminaire has low luminance at high viewing angles in all verticalplanes.

In a tenth preferred embodiment (FIG. 27), a linear distributionkinoform diffuser is affixed to a curved substrate that is positionedbelow and oriented parallel to the major axis of a linear light sourcesuch that it both diffuses the emitted light in a plane parallel to thelight source axis and preferentially redirects it downwards towards thework plane. The luminaire has low luminance at high viewing angles inall vertical planes, while the curved central region provides a linearbatwing luminous intensity distribution.

In an eleventh preferred embodiment (FIG. 29), a linear distributionkinoform diffuser with a curved central region is positioned below alinear light source such that it both diffuses the emitted light andpreferentially redirects it downwards towards the work plane. Theluminaire has low luminance at high viewing angles in all verticalplanes, while the curved central region in combination with the planarregions provides a linear batwing luminous intensity distribution.

In a twelfth preferred embodiment (FIG. 30), a linear or ellipticaldistribution kinoform diffuser is positioned above and oriented parallelto the major axis of a linear light source such that it diffuses theemitted light in a plane parallel to the light source. The luminairesubstantially eliminates lamp shadows due to uneven illumination of theceiling above the lamp sockets (FIG. 31).

In a thirteenth preferred embodiment (FIG. 32), a linear or ellipticaldistribution kinoform diffuser with a curved central region ispositioned below and oriented perpendicular to the major axis of alinear light source such that it both diffuses the emitted light in aplane perpendicular to the light source axis and preferentiallyredirects it downwards towards the work plane. The luminaire has lowluminance at high viewing angles in all vertical planes, while thecurved central region provides a linear batwing luminous intensitydistribution with essentially complete elimination of the light sourceimage from all viewing angles.

In a fourteenth preferred embodiment (FIG. 33), a circular distributionkinoform diffuser with a curved central region is positioned below apoint light source such that it both diffuses the emitted light andpreferentially redirects it downwards towards the work plane. Theluminaire has low luminance at high viewing angles in all verticalplanes, while the curved central region provides a circular batwingluminous intensity distribution with essentially complete elimination ofthe light source image from all viewing angles.

In a fifteenth preferred embodiment (FIG. 34), a reflective kinoformdiffuser with a linear or an elliptical distribution is positioned aboveand oriented parallel to a linear light source such that it bothdiffuses the emitted light in a plane perpendicular to the light sourceaxis and preferentially redirects downwards towards the work plane. Theluminaire has low luminance at high viewing angles in the vertical planeperpendicular to the light source axis.

In a sixteenth preferred embodiment (FIG. 35), a reflective kinoformdiffuser with a circular distribution may be positioned above a linearor point light source such that it both diffuses the emitted light andpreferentially redirects it downwards towards the work plane.

In a seventeenth preferred embodiment (FIG. 36), a skylight or windowconsisting of a transmissive kinoform diffuser both diffuses andpreferentially redirects diffused sunlight downwards towards the workplane. It performs the function of a motor-driven heliostat without theneed for active control devices.

Additional objects and advantages of the disclosed embodiments will beapparent from the following detailed description of preferredembodiments thereof which proceeds with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of the scattering of incident beamsof collimated light by prior art transmissive and reflective diffusers.

FIG. 2 is a schematic illustration of the cross-sections of thescattered light beam distributions from a prior art isotropic (circular)diffuser, elliptical anisotropic diffuser, and substantially linearanisotropic diffuser.

FIGS. 3A and 38 are schematic illustrations of off-axis beamdistributions for transmissive kinoform diffusers designed in accordancewith the invention with their surface relief patterns facing,respectively, away from and toward the direction of incident light.

FIG. 4 is a schematic illustration of an off-axis beam distribution fora reflective kinoform diffuser designed in accordance with theinvention.

FIG. 5 shows a prior art single-beam holographic setup for the recordingof kinoform diffusers.

FIG. 6 shows a photomicrograph of a typical recorded laser specklepattern produced by the prior art holographic setup of FIG. 5.

FIG. 7 shows the expected negative exponential laser speckle intensityas a function of scattering angle from a prior art single-exposurekinoform diffuser.

FIGS. 8A, 88, 8 e, and 80 show the beam distributions for four classesof kinoform diffusers, the surface relief patterns of which are facingthe incident beam.

FIG. 8E shows the off-axis transmittance of an incident beam with anincidence angle of 60 degrees.

FIG. 8F show the off-axis retroreflectance of an incident beam with anincidence angle of 75 degrees.

FIG. 9 shows the probability distribution of the summed laser speckleintensity as a function of N uncorrelated prior art laser specklepattern exposures.

FIG. 10 shows a photomicrograph of a circular distribution kinoformdiffuser constructed in accordance with the invention to exhibit auniform beam distribution.

FIG. 11 shows a photomicrograph of a linear distribution kinoformdiffuser constructed in accordance with the invention to exhibit auniform beam distribution.

FIG. 12 shows a photomicrograph of a circular distribution kinoformdiffuser constructed in accordance with the invention to exhibit anannular beam distribution.

FIG. 13A illustrates the circular (isotropic) “batwing” luminousintensity distribution used to provide even illuminance distribution ona work plane or ceiling. The distribution is the same for all verticalplanes.

FIG. 13B illustrates a circular batwing luminous intensity distributionwith sharp cutoff characteristics.

FIG. 13C illustrates a substantially linear (anisotropic) batwingluminous intensity distribution used to provide even illuminancedistribution for indoor hallways and exterior roadways. The distributionvaries for different vertical planes, where the Odegree vertical planeis by convention ([IESNA 2000]) parallel to the major axis of the lampor luminaire.

FIG. 130 is a diagram showing two exemplary vertical planes set indifferent locations established by different angular displacements (0°,90°) about a common axis perpendicular to a longitudinal axis of alinear light source and the place of diffusion.

FIG. 14 illustrates for a ceiling-mounted luminaire the typical range ofviewing angles over which designers attempt to minimize glare.

FIG. 15 illustrates a luminaire with a linear light source utilizing alinear or an elliptical distribution kinoform diffuser to minimize glareat high viewing angles in the vertical plane perpendicular to the lightsource axis.

FIG. 16 illustrates a luminaire with a point light source utilizing acircular or an elliptical distribution kinoform diffuser to minimizeglare at high viewing angles.

FIG. 17 illustrates a luminaire with a linear light source utilizing alinear or an elliptical distribution kinoform diffuser to minimize glareat high viewing angles in the vertical plane parallel to the lightsource axis.

FIG. 18 illustrates a luminaire with a point light source utilizing alinear or an elliptical distribution kinoform diffuser to minimize glareat high viewing angles in the plane parallel to the plane of diffusion.

FIG. 19 illustrates a luminaire with a point light source utilizing aseries of wedge-shaped linear or elliptical distribution kinoformdiffusers to minimize glare at high viewing angles.

FIG. 20 illustrates a luminaire with a linear light source utilizing adiffuser with a transparent central region and exhibiting controllablediffusion characteristics to provide a linear batwing luminous intensitydistribution.

FIG. 21 illustrates a luminaire with a point light source utilizing acircular distribution diffuser with a transparent central region andexhibiting controllable diffusion characteristics to provide a circularbatwing luminous intensity distribution.

FIG. 22 illustrates the luminous intensity distribution provided by theluminaire shown in FIG. 21. The distribution varies with the distance dbetween the light source and the diffuser.

FIG. 23A illustrates a luminaire with a linear light source utilizing aninwardly folded linear distribution kinoform diffuser to provide aluminous intensity distribution with improved glare reduction at highviewing angles in all vertical planes.

FIG. 238 illustrates the light source images seen through the luminaireshown in FIG. 23A for two different vertical viewing angles.

FIG. 24 illustrates the luminous intensity distribution provided by theluminaire shown in FIG. 23A. The zero-degree plane is parallel to themajor axis of the light source.

FIG. 25A illustrates a luminaire with a linear light source utilizing anoutwardly folded linear distribution kinoform diffuser to provide abatwing luminous intensity distribution with improved glare reduction athigh viewing angles in all vertical planes.

FIG. 25B illustrates the light source images seen through the luminaireshown in FIG. 25A for two different vertical viewing angles.

FIG. 26 illustrates the luminous intensity distribution provided by theluminaire shown in FIG. 25A. The zero-degree plane is parallel to themajor axis of the light source.

FIG. 27 illustrates a luminaire with a linear light source utilizing alinear distribution kinoform diffuser to provide a linear batwingluminous intensity distribution with improved glare reduction at highviewing angles in all vertical planes.

FIG. 28 illustrates the luminous intensity distribution provided by theluminaire shown in FIG. 27. The zero-degree plane is parallel to themajor axis of the light source.

FIG. 29 illustrates a luminaire with a linear light source utilizing alinear distribution kinoform diffuser with a curved central region toprovide a linear batwing luminous intensity distribution with improvedglare reduction at high viewing angles in all vertical planes.

FIG. 30 illustrates a luminaire with a linear light source utilizing acurved linear distribution kinoform diffuser to provide a linear batwingluminous intensity distribution with elimination of lamp shadows.

FIG. 31 illustrates the elimination of lamp socket shadows using amultiplicity of linear light sources with a common kinoform diffuser.

FIG. 32 illustrates a luminaire with a linear light source utilizing alinear or an elliptical distribution diffuser with a curved centralregion, the diffuser exhibiting controllable diffusion characteristicsto provide a linear batwing luminous intensity distribution withimproved glare reduction at high viewing angles in the vertical planeperpendicular to the light source axis and light source imageelimination from all viewing angles.

FIG. 32-1 shows the diffused light beam distributions produced by thegenerally planar side portions and the curved center portion of thepreferred embodiment of FIG. 32.

FIG. 32-2 shows a luminous intensity distribution with two distinctpeaks formed by the side portions of the preferred embodiment of FIG. 32when its curved center portion is blocked.

FIG. 32-3 shows a generally lambertian luminous intensity distributionproduced by the curved center portion of the preferred embodiment ofFIG. 32.

FIG. 32-4 shows a batwing luminous intensity distribution of thepreferred embodiment of FIG. 32.

FIG. 32-5 is an isometric view of an alternative embodiment of theluminaire of FIG. 32, in which the curved center portion is replaced bya planar center diffuser positioned beneath the side portions that aretilted slightly away from the light source.

FIGS. 32-6A and 32-68 show the batwing luminous intensity distributions,together with side elevation views of corresponding implementations, ofthe alternative embodiment of FIG. 32-5 at, respectively, smaller andlarger side portion tilt angles relative to horizontal.

FIG. 33 illustrates a luminaire with a point light source utilizing acircular distribution diffuser with a curved central region, thediffuser exhibiting controllable diffusion characteristics to provide acircular batwing luminous intensity distribution with improved glarereduction at high viewing angles and light source image elimination fromall viewing angles.

FIGS. 34 and 35 illustrate luminaires utilizing reflective kinoformdiffusers of, respectively, a linear or an elliptical distribution typeand a circular distribution type.

FIG. 36 illustrates a skylight or window utilizing a transmissivekinoform diffuser that performs the function of a motor-driven heliostatin the absence of active control devices.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A kinoform diffuser made in accordance with this disclosure is composedof a complex surface relief pattern that produces controllable diffusioncharacteristics with off-axis transmittance and reflectance properties,elimination of zero-order beam, and freedom from spectral dispersionunder achromatic illumination.

Prior art techniques as described by Gray enable the fabrication ofsurface-relief holographic diffusers that exhibit elimination ofzero-order beam and freedom from spectral dispersion under achromaticillumination. However, on page 767, Gray states: “The incoherentsummation of uncorrelated speckle patterns . . . can be carried out bymaking a series of exposures of a photoresist film to the far-fieldspeckle pattern from a ground glass diffuser, moving a new part of theground glass into the laser beam for each exposure.” As noted by Dainty,each laser speckle pattern is uncorrelated with respect to the otherpatterns.

Laboratory experiments performed by the applicants have revealed certainadvantages to moving the photosensitive plate rather than the groundglass diffuser between exposures. The laser speckle pattern remainsunchanged, and so the recorded patterns are spatially autocorrelated.

The incoherent summation of autocorrelated speckle patterns has not beentheoretically analyzed in the published literature. However, applicants'laboratory experiments have revealed that the resultant kinoformdiffuser beam distribution is not necessarily characterized by asubstantially Gaussian function. Various combinations of the number ofexposures and movement of the photosensitive plate between saidexposures contribute to the production of kinoform diffusers withuniform and annular beam distributions as shown in FIGS. 8A, 8B, 8C, and8D. Unlike Gaussian distributions, these beam distributions exhibitgreatly reduced scattering outside of the specified range of angles.Movement of the photosensitive plate between exposures also enables thefabrication of kinoform diffusers that exhibit elimination of zero-orderbeam and freedom from spectral dispersion under achromatic illumination.

As described by Gray and others, surface-relief optical diffusersrequire that their surface relief height distributions be directlyproportional to the intensity distributions of the recorded laserspeckle patterns. When viewed with a scanning electron microscope, thesesurface relief patterns resemble a series of smoothly rolling hills.However, the applicants have learned through laboratory experiments thata complex surface relief pattern of pebbles (as shown in FIG. 10)significantly contributes to the production of circular (isotropic)kinoform diffusers with uniform beam distributions, as shown in FIG. 8A.Similarly, a complex surface relief pattern of “corrugations” (as shownin FIG. 11) significantly contributes to the production of ellipticaland linear (anisotropic) kinoform diffusers with uniform beamdistributions, as shown in FIG. 8B.

Applicants have also learned through laboratory experiments that acomplex surface relief pattern of “pits” (resembling an impression ofthe pebbled surface shown in FIG. 10) also significantly contribute tothe production of circular (isotropic) kinoform diffusers with uniformbeam distributions, as shown in FIG. 8A.

The applicants have further learned through laboratory experiments thata pattern of substructures or sub-elements formed on the surfaces of thepebbles (as shown in FIG. 12), pits, or corrugations significantlycontributes to the production of kinoform diffusers with annular beamdistributions, as shown in FIGS. 8C and 8D. FIGS. 10-12 show that thecomplex surface relief patterns of light scattering elements in the formof pebbles, pits, or corrugations are characterized by overlapping lightscattering elements and interstitial cavities among neighboring ones ofthe light scattering elements.

The disclosed embodiments are preferably implemented with the use ofpositive photoresist materials such as Shipley 1818 from Shipley Company(Marlborough, Mass.). These materials typically have nonlinearcharacteristic responses to the exposing light. Unlike prior arttechniques as taught by Gray and others, the invention exploits thisproperty by using a combination of controlled parameters for thepreparation, exposure, and development of the photoresists and arelatively thick photoresist layer that can be etched to a depth ofmultiple wavelengths of visible light.

The surface relief features of pits or corrugations are apparentlyformed by the exposure of the photoresist material to a volumetriccross-section of the three-dimensional laser speckle pattern. Thephotoresist material is then processed to etch away the exposed portionsand produce the three-dimensional scattering elements. Negativephotoresist materials such as Microchem SU-8 available from MicrochemCorporation (Newton, Mass.) may be used to produce pebbles rather thanpits.

The photoresist is applied to a glass substrate using known spin coatingtechniques. The coating thickness is determined by the photoresistviscosity and the rotation speed, but is generally between 3.0 and 12.0microns. A single layer of photoresist or multiple layers ofphotoresists with varying formulations may be usefully applied to thesubstrate to achieve composite photoresists with desirable non-linearcharacteristic responses.

The photoresist characteristic response is partly dependent upon theconcentration of solvent (typically propylene glycol monomethyl etheracetate) remaining in the material at the time of exposure. It may benecessary to “prebake” the photoresist coating at an elevatedtemperature to remove the majority of the solvent through evaporationwhile ensuring that the photoactive component of the resist is notthermally decomposed. The bake time, temperature, humidity, and airfloware carefully controlled during this process to achieve consistent anddesirable results.

The photoresist is then exposed to one or a multiplicity of laserspeckle patterns. With reference to FIG. 5, the coherent laser beamproduced by beam expansion lenses 52 and 54 can be parallel, convergent,or divergent, depending upon the desired kinoform diffuser beamdistribution. A non-uniform laser beam intensity profile may also beusefully employed to modify the resultant kinoform diffuser beamdistribution. The photoresist may be uniformly exposed prior to exposureto the laser speckle pattern or patterns to pre-sensitize thephotoactive component.

The individual laser speckle pattern exposure times are dependent uponthe laser power, beam expansion optics, diffuser opacity, andphotoresist sensitivity. The laser power may be intentionally reduced toinduce reciprocity failure in the photoresist and thereby usefullyamplify the nonlinear effects of thin film interference exposure.Regardless, careful exposure control ensures that the maximum exposureis within the dynamic range of the processed photoresist.

Following exposure, the photoresist may optionally be subjected to a“postbake” process at an elevated temperature. This process serves toalleviate the deleterious effects of thin film interference (i.e.,standing wave) exposure within the photoresist by diffusing thephotoactive component (typically diazonaphthoquinone for positiveresists) through the resist matrix (typically a phenolic-formaldehyderesin called “novolac”). It may also be used to thermally catalyzechemical reactions, thereby amplifying the latent image. Again, the baketime, temperature, humidity, and airflow are carefully controlled toachieve consistent and desirable results.

The substructures shown in FIG. 12 appear to be produced as a result ofthin film interference exposure within the photoresist. For kinoformdiffusers where such corrugations are desirable, postbaking may nottherefore not be necessary.

The photoresist is then developed using an alkaline developer such assodium hydroxide. Commercial developers may contain proprietaryadditives for specific purposes that modify the photoresist etchingprocess. These additives may usefully modify the photoresistcharacteristic response.

There are several conventional techniques for applying the developer,including spin coating, spray development, and puddle development. Thedevelopment time and temperature, together with the developerconcentration, are parameters that affect the resultant characteristicresponse.

Following development, the photoresist may optionally be subjected to a“post-development bake” process at an elevated temperature. This processserves to harden the developed photoresist through crosslin king of thenovolac resin and to optionally modify the surface relief profilethrough softening and plastic flow.

An important attribute of photoresist processing for kinoform diffusersis the resultant contrast r (gamma), which is expressed as:

γ=1/(log₁₀(E _(max) /E _(min))),  (3)

where E_(min) is the minimum actinic exposure (measured in millijoulesper square centimeter) required to produce a photochemical reaction inthe photoactive component leading to etching, and E_(max) is the maximumactinic exposure required to produce etching of the photoresist to theunderlying substrate.

The resultant gamma is dependent upon the prebake, exposure, postbake,development, and post-development bake parameters. These parameters arein turn dependent upon the photoresist composition and developeradditives. Although skilled persons will realize that it is difficult tocharacterize the effect of these parameters in combination or predictthe results stemming from changing them, the applicants have discoveredthat the following interrelated parameters affect the resultant gamma:photoresist composition, prebaking, laser beam wavelength, laser powerand exposure times, postbaking, developer formulation, developerconcentration, development time, development temperature, andpost-development baking.

Finding an appropriate combination of process parameters that allows forthe production of kinoform diffusers with controllable non-uniform beamdistributions is a trial-and-error process. Applicants have determinedthat desirable non-uniform beam distributions can be consistently andreliably produced, and that the beam distribution parameters can beincrementally controlled. In particular, the distributions can becontinuously varied between the uniform beam distributions shown inFIGS. 8A and 88 to the non-uniform distributions shown in FIGS. 8 e and80, respectively.

The zero-order beam can be eliminated by exposing the photoresist to amultiplicity of autocorrelated laser speckle patterns. These patternsmay be produced by one or more of the following mechanical movements:shift photoresist plate perpendicular to laser beam direction; shiftdiffuser perpendicular to laser beam direction; shift photoresist plateparallel to laser beam direction; shift diffuser parallel to laser beamdirection; rotate photoresist plate about axis perpendicular to laserbeam direction; rotate diffuser about axis perpendicular to laser beamdirection; rotate photoresist plate about axis parallel to laser beamdirection; and rotate diffuser about axis parallel to laser beamdirection. In addition, the laser beam intensity profile incident uponthe diffuser can be optically modified to effect a partial decorrelationof the laser speckle pattern.

In a first preferred diffuser embodiment, a kinoform diffuser with theuniform beam distribution shown in FIG. 8A may be produced by first spincoating a glass plate with Shipley 1818 or 1827 positive photoresist.This plate is then optionally prebaked at 85 degrees C. for thirtyminutes in an oven to remove excess solvent.

The baked plate is cooled to room temperature and exposed to a laserspeckle pattern generated using the optical setup shown in FIG. 5, usingopaque mask 56 with a circular aperture 58. A 180-milliwatthelium-cadmium laser is used to illuminate the ground glass diffuser 60.

The exposed plate is then shifted in a random direction perpendicular tothe illuminating beam axis before exposing the plate to the same laserspeckle pattern. This process is repeated several times to eliminatezero-order beam transmission.

Following exposure, the plate may optionally be post-baked at 110degrees C. for five minutes in an oven to eliminate possible defectsresulting from thin film interference and thermally catalyze chemicalreactions that may amplify the latent image.

The exposed plate is developed in Shipley 303A developer diluted withwater and is then placed in a water rinse bath to stop the etchingprocess, dried, and optionally post-baked at 110 degrees C. for 60seconds.

By changing the development time, a kinoform diffuser with thenon-uniform beam distribution shown in FIG. 8 e may be produced. Varyingthe development time produces a continuous and controllable variation inthe beam distribution.

By substituting an elliptical or rectangular aperture 58 in opaque mask56, kinoform diffusers with elliptical or linear beam distributions maybe produced as shown in FIG. 8B and FIG. 80, respectively.

In a second preferred diffuser embodiment, a digitized representation ofthe three-dimensional surface relief pattern comprising the kinoformdiffuser is computer-generated from mathematical models or obtained froma scanning confocal microscope. This representation is then fabricatedin a photopolymerizable resin using known stereolithography techniquesas described in Maruo, S. et al., “Three-Dimensional Microfabricationwith Two-Photon-Absorbed Photopolymerization,” Optics Letters 22(2):132-134 (Jan. 15, 1997), Cumpston, B. J., et aI, “Two-PhotonPolymerization Initiators for Three-Dimensional Optical Data Storage andMicrofabrication,” Nature 398(4):51-54 (Mar. 4, 1999), and Galajda, P.,and P. Ormos, “Complex Micromachines Produced and Driven by Light,”Applied Physics Letters 78(2):249-251 (Jan. 8, 2001). As described, forexample, in the publication of Galajda and Ormos, a layer of Norland NOA63 optical adhesive from Norland Products (Cranbury, N.J.) is applied toa substrate. The 514 nm line output of a 20 milliwatt argon laser isthen focused to a 0.5 urn diameter spot within said layer to initiatetwo-photon polymerization. Moving the substrate along a preprogrammedtrajectory with a P3D 20-100 three-axis piezo translation stage fromLinos Photonics (Milford, Mass.) allows arbitrary three-dimensionalmicrostructures to be fabricated. The unexposed resin is then removed bydissolving in acetone.

Skilled persons will appreciate that the surface relief patternresponsible for the optical characteristics of a transmissive kinoformdiffuser is the boundary between two transparent media with differentindices of refraction. The claimed invention encompasses, therefore, anyembodiment in which a protective layer of a transparent medium with adifferent refractive index is applied to the surface of a kinoformdiffuser. As an example, a transmissive kinoform diffuser made from apolymerized optically transparent resin with a refractive index of 1.56could be coated with fluoropolymer such as Teflon AF from E.I. du Pontde Nemours and Company with a refractive index of 1.30.

Kinoform diffusers as described above are microscopic surface reliefpatterns applied to one or both surfaces of substantially transparentoptical elements such as glass or plastic substrates. Variousmanufacturing methods may be employed, including but not limited to: a)casting and curing of ultraviolet-polymerizable resin films onto glassor plastic substrates; b) embossing plastic substrates or films; c)vacuum-forming plastic substrates; d) lamination of plastic films withkinoform diffusers onto glass or plastic substrates; e) bulk casting orinjection molding of glass or plastic substrates; and f) casting orembossing of sol gel materials onto glass or plastic substrates. Theseoptical elements are then used in the manufacture of luminaires inaccordance with the design principles disclosed herein.

Embodiments of light control devices, including luminaires, implementedwith diffusers exhibiting controllable diffusion characteristics, aredescribed below.

Skilled persons will appreciate that such kinoform diffusers may performadditional light control functions because of their bulk shape ormacroscopic surface relief patterns generated by embossing, casting,vacuum-forming, injection molding, or other manufacturing techniques.Examples include kinoform diffusers applied to radially symmetric andcylindrical lenses, lens arrays, microlens arrays, and Fresnel lenses.Antireflection coatings may also be applied to reduce unwantedreflections from the surfaces of transparent optical elements such asglass or plastic substrates. Moreover, skilled persons will appreciatethat such substantially transparent diffusers may be coated on one orboth surfaces with partly reflective films such as vacuum depositedaluminum to further control the distribution of light without negatingthe design principles of the present invention as disclosed herein.

In a first preferred embodiment (FIG. 15), a curved transparentsubstrate 80 is positioned below a linear light source 76 having alongitudinal or major axis 78, with a kinoform diffuser 82 applied tothe side of substrate 80 facing away from light source 76. Kinoformdiffuser 82 is oriented such that its plane of diffusion 74 isperpendicular to major axis 78 of light source 76.

Kinoform diffuser 82 will diffuse an incident ray of light 84 emitted bylight source 76 into the luminous flux distribution schematicallyindicated by a set of rays 88. In accordance with the novel controllablediffusion characteristics of kinoform diffusers described above,luminous flux distribution 88 (that is, the diffusion characteristics)may be varied in a controlled manner during production of the kinoformdiffuser to provide an optimum luminous intensity distribution for theluminaire, as determined by its intended application.

In addition, the diffusion characteristics of kinoform diffuser 82 maybe spatially varied according to the horizontal distance of the diffuserfrom major axis 78 of light source 76, with different linear segments ofthe kinoform diffuser parallel to the light source axis having differentdiffusion characteristics.

Also in accordance with the novel off-axis transmission properties ofkinoform diffusers, the direction of maximum intensity of luminous fluxdistribution 88 is offset from the direction of incident ray of light 84by an angle 8 towards a local surface normal 86 of kinoform diffuser 82at the point of intersection, where said angle may be varied in acontrolled manner during production of kinoform diffuser 82. The lightemitted by light source 76 at high viewing angles is, therefore,redirected downwards towards nadir 90. This advantageously increases theilluminance of the work plane and simultaneously reduces the luminanceof the luminaire at high viewing angles in horizontal directionssubstantially perpendicular to the light source axis, which therebyreduces its glare.

These advantages are most effectively realized with a lineardistribution kinoform diffuser. However, an elliptical distributionkinoform diffuser may advantageously be used to increase the apparentwidth of light source 76 when viewed directly through kinoform diffuser92 from directions that are substantially perpendicular to the lightsource axis.

In a second preferred embodiment (FIG. 16), a transparent substrate 98is positioned below a point light source 92, with a circular orelliptical distribution kinoform diffuser 100 applied to the side ofsaid substrate facing away from light source 92.

Kinoform diffuser 100 will diffuse incident rays of light 94 and 96emitted by light source 92 into the luminous flux distributionsschematically indicated by the respective sets of rays 102 and 104.Similar to the first preferred embodiment, luminous flux distributions102 and 104 may be varied in a controlled manner during production ofkinoform diffuser 100. The diffusion characteristics of kinoformdiffuser 100 may also be spatially varied according to the radialdistance of the diffuser from the vertical axis of light source 92.

Also in accordance with the novel off-axis transmission properties ofkinoform diffusers, the direction of maximum intensity of luminous fluxdistribution 104 is offset from the direction of incident ray of light96 by an angle e towards a surface normal 106 of kinoform diffuser 100,where said angle may be varied in a controlled manner during productionof kinoform diffuser 100. The light emitted by light source 92 at highviewing angles is, therefore, redirected downwards towards nadir. Thisadvantageously increases the illuminance of the work plane andsimultaneously reduces the luminance of the luminaire at high viewingangles for all vertical planes.

These advantages are most effectively realized with a circulardistribution kinoform diffuser. However, an elliptical distributionkinoform diffuser may advantageously be used to generate an ellipticalluminous intensity distribution for the luminaire, as determined by itsintended application.

In a third preferred embodiment (FIG. 17), a transparent substrate 116is positioned below a linear light source 108 having a major axis 110,with a kinoform diffuser 118 applied to the side of substrate 116 facingaway from light source 108 Kinoform diffuser 118 is oriented such thatits plane of diffusion 120 is parallel to the major axis of light source108.

Kinoform diffuser 118 will diffuse an incident ray of light 114 emittedby light source 108 into the luminous flux distributions schematicallyindicated by a ray 122. In accordance with the novel off-axistransmission properties of kinoform diffusers, the direction of maximumintensity of luminous flux distribution 122 is offset from the directionof incident ray of light 114 by an angle 8 towards a surface normal 124of kinoform diffuser 118, where said angle may be varied in a controlledmanner during production of kinoform diffuser 118. The light emitted bylight source 108 at high viewing angles in the vertical plane parallelto the light source axis is, therefore, redirected downwards towardsnadir 112. This advantageously increases the illuminance of the workplane and simultaneously reduces the luminance of the luminaire at highviewing angles in horizontal directions substantially parallel to thelight source axis. (Skilled persons will appreciate that this advantagecannot be achieved using conventional diffusers without the use ofbaffles or louvers.)

In a fourth preferred embodiment (FIG. 18), a transparent substrate 132is positioned below a point light source 126, with a linear distributionkinoform diffuser 134 applied to the side of substrate 132 facing awayfrom light source 126.

Kinoform diffuser 134 will diffuse a ray of light 130 emitted by lightsource 126 into the luminous flux distribution schematically indicatedby a ray 140. In accordance with the novel controllable diffusioncharacteristics of kinoform diffusers, said luminous flux distributionsmay be varied in a controlled manner during production of kinoformdiffuser 134. In addition, the diffusion characteristics of kinoformdiffuser 134 may be spatially varied according to its radial distancefrom the vertical axis 128 of light source 126.

Also in accordance with the novel off-axis transmission properties ofkinoform diffusers, the direction of maximum intensity of luminous fluxdistribution 140 is offset from the direction of ray of light 130 by anangle 8 towards a surface normal 138 of kinoform diffuser 134, wheresaid angle may be varied in a controlled manner during production ofkinoform diffuser 134. The light emitted by light source 126 at highviewing angles is, therefore, redirected downwards towards nadir alongvertical axis 128. This advantageously increases the illuminance of thework plane and simultaneously reduces the luminance of the luminaire athigh viewing angles for horizontal directions substantially parallel tothe plane of diffusion 136.

The fourth preferred embodiment (FIG. 18) is similar in concept to thesecond preferred embodiment (FIG. 16); the difference is that the lineardiffusion characteristics of kinoform diffuser 134 provides asubstantially linear (anisotropic) luminous intensity distribution forthe luminaire (FIG. 2, rightmost diagram).

In a fifth preferred embodiment (FIG. 19), a transparent substrate 148is positioned below a point light source 142, with a kinoform diffuser150 composed of a multiplicity of wedge-shaped linear or ellipticaldistribution kinoform diffuser segments 152 applied to the side ofsubstrate 148 facing away from light source 142. Each kinoform diffusersegment 152 is oriented such that its plane of diffusion 158 is radialto a vertical axis 144 of light source 142.

Kinoform diffuser segments 152 will diffuse a ray of light 146 emittedby light source 142 into the luminous flux distribution schematicallyindicated by a ray 156.

In accordance with the novel controllable diffusion characteristics ofkinoform diffusers, luminous flux distribution 156 may be varied in acontrolled manner during production of kinoform diffuser 150. Inaddition, the luminous flux distribution characteristics of kinoformdiffuser segments 152 may be varied according to the radial distance ofdiffuser 150 from vertical axis 144 of light source 142.

Also in accordance with the novel off-axis transmission properties ofkinoform diffusers, the direction of maximum intensity of luminous fluxdistribution 156 is offset from the direction of incident ray of light146 by an angle 8 towards a surface normal 154 of kinoform diffusersegments 152, where said angle may be varied in a controlled mannerduring production of kinoform diffuser 150. The light emitted by lightsource 142 at high viewing angles is, therefore, redirected downwardstowards nadir along vertical axis 144. This advantageously increases theilluminance of the work plane and simultaneously reduces the luminanceof the luminaire at high viewing angles for all horizontal directions.

The fifth preferred embodiment (FIG. 19) is similar in concept to thesecond preferred embodiment (FIG. 16); the difference is that the linearor elliptical distributions of the radially oriented kinoform diffusersegments 152 provide more precisely controllable diffusion. Inparticular, the ability to limit diffusion to a specific vertical anglefor each emitted ray 146 enables the design of luminaires whose luminousintensity distributions exhibit sharp cutoffs at high viewing angles(FIG. 14).

These advantages are most effectively realized with a lineardistribution kinoform diffuser. However, an elliptical distributionkinoform diffuser may advantageously be used to generate a radiallysymmetric luminous intensity distribution for the luminaire thatexhibits more moderate cutoff characteristics, as determined by itsintended application.

In a sixth preferred embodiment (FIG. 20), a transparent substrate 160is positioned a distance d below a linear light source 162 having amajor axis 164, with a kinoform diffuser 166 applied to the peripheralregions of substrate 160 on the side facing away from light source 162.A central region 168 is left unobstructed. Kinoform diffuser 166 may beoriented such that its plane of diffusion is parallel to major axis 164of light source 162, as in the first preferred embodiment (FIG. 15), orperpendicular to the major axis, as in the third preferred embodiment(FIG. 17). Alternatively, a circular distribution kinoform diffuser maybe employed.

A ray of light 170 emitted by light source 162 will pass through centralregion 168 of transparent substrate 160 without diffusion, whilekinoform diffuser 166 will diffuse a ray of light 172 into the luminousflux distribution schematically indicated by a set of rays 174.

The sixth preferred embodiment (FIG. 20) is distinguished from the first(FIG. 15) and third (FIG. 17) preferred embodiments by the presence oftransparent central region 168, which provides for greater control overthe luminous intensity distribution of the luminaire without reducingthe luminaire efficiency.

An additional advantage of the sixth preferred embodiment is that theluminous intensity distribution of the luminaire can be varied bychanging the distance d from light source 162 to transparent substrate160.

In a seventh preferred embodiment (FIG. 21), a transparent substrate 176is positioned a distance d from a point light source 178, with akinoform diffuser 180 applied to the peripheral regions of substrate 176on the side facing away from light source 178. A central region 182 isleft unobstructed. Kinoform diffuser 180 may be as disclosed in thesecond (FIG. 16), fourth (FIG. 18), or fifth (FIG. 19) preferredembodiments. The presence of transparent central region 182 provides forgreater control over the luminous intensity distribution of theluminaire without reducing the luminaire efficiency.

A ray of light 184 emitted by light source 178 will pass through centralregion 182 of transparent substrate 176 without diffusion, whilekinoform diffuser 180 will diffuse ray of light 186 into the luminousflux distribution schematically indicated by a set of rays 188.

An additional advantage of the seventh preferred embodiment is that theluminous intensity distribution of the luminaire can be varied bychanging the distance d from light source 178 to kinoform diffuser 180(FIG. 22).

In an eighth preferred embodiment (FIG. 23A), an inwardly foldedtransparent substrate 198 formed of two generally planar portionsarranged in a V-shape is positioned below a linear light source 192having a major axis 194, with linear or elliptical distribution kinoformdiffuser portions 196 applied to either side of substrate 198. (Thekinoform diffuser is shown on the side facing towards light source 192for the purposes of illustration. This orientation offers better controlof the photometric properties of the eighth preferred embodiment.)Kinoform diffuser portions 196 are oriented such that their planes ofdiffusion 200 are parallel to major axis 194 of light source 192.

When the luminaire is viewed from nadir 190, the image of light source192 appears normally as shown in schematic view 202 (FIG. 238). However,when the luminaire is viewed at increasing angles in the vertical planeintersecting the major light source axis (by convention termed theO-degree vertical plane), the image of light source 192 appears todecrease in width, as shown in schematic view 204 (FIG. 238).

The light source image disappears at a view angle that is determined bythe fold angle 8, the off-axis transmission properties of kinoformdiffuser 196, which side of the substrate 198 diffuser 196 is appliedto, the length of substrate 198, and the distance from the luminaire tothe viewer.

An advantage of the eighth preferred embodiment is that the luminousintensity distribution of the luminaire has a sharp cutoff angle in allvertical planes (FIG. 24). (Skilled persons will appreciate that thisadvantage cannot be achieved in the O-degree plane using conventionaldiffusers without the use of baffles or louvers.)

In a ninth preferred embodiment (FIG. 25A), an outwardly foldedtransparent substrate 212 formed of two generally planar portionsarranged in a V-shape is positioned below a linear light source 208having a major axis 210, with linear or elliptical distribution kinoformdiffuser portions 214 applied to either side of substrate 212. (Kinoformdiffuser portions 214 are shown on the side facing toward light source208 for the purposes of illustration.) Kinoform diffuser portions 214are oriented such that their planes of diffusion 206 are parallel tomajor axis 210 of light source 208.

When the luminaire is viewed from nadir 216, the image of light source208 appears normally as shown in schematic view 218 (FIG. 25B). However,when the luminaire is viewed at increasing angles in the a-degreevertical plane, light source 208 appears to divide into two images, asshown in schematic view 220 (FIG. 25B).

The light source images disappear at a view angle that is determined bythe fold angle e, the off-axis transmission properties of kinoformdiffuser 214, which side of the substrate 212 diffuser 214 is appliedto, the length of substrate 212, and the distance from the luminaire tothe viewer.

An advantage of the ninth preferred embodiment is that the luminousintensity distribution of the luminaire has a sharp cutoff angle in allvertical planes. Another advantage of the ninth preferred embodiment isthat it provides a desirable batwing luminous intensity distribution inall vertical planes (FIG. 26) by providing two light source images.(Skilled persons will appreciate that this advantage cannot be achievedin the a-degree plane using conventional diffusers without the use ofbaffles or louvers.)

In a tenth preferred embodiment (FIG. 27), two curved transparentsubstrate portions 228 arranged in the general form of a U-shape arepositioned below a linear light source 222 having a major axis 224.Opaque light shields 226 are positioned adjacent different ones ofsubstrate portions 228 and on either side of light source 222, withlinear or elliptical distribution kinoform diffuser portions 230 appliedto substrate portions 228 on the sides facing towards light source 222.Diffuser portions 230 are oriented such that their planes of diffusion232 are parallel to major axis 224 of light source 222.

The advantages of the tenth preferred embodiment (FIG. 27) are the sameas those of the ninth preferred embodiment (FIG. 25A). In addition, thecurvatures of substrate portions 228 may be varied to provide furthercontrol over the luminous intensity distribution characteristics of theluminaire. In particular, they may be designed to produce a batwingluminous intensity distribution with an extremely sharp cutoff angle(FIG. 28).

In an eleventh preferred embodiment (FIG. 29), two generally planartransparent substrate portions 234 are positioned below a linear lightsource 236 having a major axis 238, with preferred linear or ellipticaldistribution kinoform diffuser portions 240 applied to substrateportions 234 on the sides facing away from light source 236. Kinoformdiffuser portions 240 are oriented such that their planes of diffusion242 are perpendicular to major axis 238 of light source 236. Although akinoform diffuser is preferred for diffuser portions 240, a batwingluminous intensity pattern can be achieved with diffuser portions 240made of other diffuser material that results in diffused light at arange of exit angles that is narrower than a range of angles of incidentlight.

In addition, two curved transparent substrate portions 244 arranged inthe general form of a U-shape are positioned below light source 236,with a linear or an elliptical distribution kinoform diffuser portions246 applied to substrate portions 244 on the sides facing towards lightsource 236. Kinoform diffuser portions 246 are oriented such that theirplanes of diffusion 248 are parallel to major axis 238 of light source236.

The eleventh preferred embodiment (FIG. 29) combines the advantages ofthe sixth (FIG. 20) and tenth (FIG. 27) preferred embodiments.

In a twelfth preferred embodiment (FIG. 30), a curved transparentsubstrate 250 is positioned above a linear light source 252 having amajor axis 254, with a linear or an elliptical distribution kinoformdiffuser 256 applied to substrate 250 on the side facing away from lightsource 252. Kinoform diffuser 256 is oriented such that its plane ofdiffusion 258 is parallel to major axis 254 of light source 252.

An advantage of the twelfth preferred embodiment is illustrated in FIG.31, where a luminaire composed of a continuous length of kinoformdiffuser 260 is positioned parallel to and above two linear fluorescentlamps 262, and located a distance d below a ceiling 264. The diffusionof light parallel to the light source axes eliminates the dark area(referred to as a “lamp socket shadow”) on the ceiling directly abovethe lamp sockets that would result without kinoform diffuser 260.

In a thirteenth preferred embodiment (FIG. 32), a transparent substratecomposed of two generally planar portions 266 separated by a generallycentrally located curved portion 268 is positioned below a linear lightsource 270 having a longitudinal axis 272. Preferably, a linear or anelliptical distribution kinoform diffuser 274 is applied to thesubstrate on the side facing away from light source 270. Kinoformdiffuser 274 is oriented such that its plane of diffusion 276 isperpendicular to major axis 272 of light source 270.

The advantages of the thirteenth preferred embodiment (FIG. 32) are thesame as those of the eleventh preferred embodiment (FIG. 29).

FIG. 32-1 shows the diffused light beam distributions produced bygenerally planar side portions or panels 266 and curved center portion268. High-angle light rays 270 a, 270 b, 270 c, 270 d, 270 e, and 270 f,incident on light entrance surfaces 266-1 of side portions 266 producecorresponding respective diffused light beam distributions 271 a, 271 b,271 c, 271 d, 271 e, and 271 f propagating from light exit surfaces266-2. Each of diffused light beam distributions 271 a-271 f has a lightintensity peak ray that propagates from its light entrance surface at anexit angle relative to the exit surface normal. The exit angle of thelight intensity peak ray of each of diffused light beam distributions271 a-271 f is less than the angle of incidence of its correspondinglight ray of high-angle light rays 270 a-270 f relative to the entrancesurface normal. FIG. 32-2 demonstrates, with curved center portion 268blocked, how light passing through side portions 266 forms a luminousintensity distribution 266 a with two distinct peaks. Luminous intensitydistribution 266 a has peaks 266P1 and 266 pz viewed at azimuthal anglesof 270 degrees and 90 degrees, respectively, in the directionperpendicular to major axis 272 of light source 270.

Light rays 270 g, 270 h, and 270 i incident on light entrance surface268-1 of curved center portion 268 produce corresponding respectivediffused light beam distributions 271 g, 271 h, and 271 i propagatingfrom light exit surface 268-2. Each of diffused light beam distributions271 g, 271 h, and 271 i has a light intensity peak ray that tracks thepropagation direction of its corresponding light ray 270 g, 270 h, and270 i. Curved center portion 268 facing away from light source 270contributes a generally lambertian luminous intensity distribution 268a, as shown in FIG. 32-3, that is similar to the luminous intensitydistribution of light source 270.

The diffused light beam distribution contribution of curved centerportion 268 combined with the diffused light beam distributioncontributions of side portions 266 produce a batwing luminous intensitydistribution 274 a. FIG. 32-4 shows luminous intensity distribution 274a having light intensity peaks 274 p 1 and 274 p 2 viewed at azimuthalangles of 270 degrees and 90 degrees, respectively, in the directionperpendicular to major axis 272 of light source 270.

Because it contributes a generally lambertian luminous intensitydistribution, curved center portion 268 can be replaced by a diffuserthat produces a luminous intensity distribution similar to distribution268 a shown in FIG. 32-3. Although a kinoform diffuser is preferred forside portions 266, a batwing luminous intensity pattern can be achievedwith side portions 266 made of other diffuser material that results indiffused light at a range of exit angles that is narrower than a rangeof angles of incident light. Moreover, side portions 266 can be tiltedeither toward or away from light source 270. Tilting side portions 266away from light source 270 produces a batwing luminous intensitydistribution with peaks 274P1 and 274P2 at lower angles (see FIG.32-6B), and tilting side portions 266 toward light source 270 produces abatwing luminous intensity distribution with peaks 274P1 and 274P2 athigher angles (see FIG. 32-6A).

FIG. 32-5 is an isometric view of an alternative embodiment of theluminaire of FIG. 32, in which curved center portion 268 is replaced bya planar center diffuser portion 268-10 positioned beneath side portions266 that are tilted slightly away from light source 270. (Although it isshown placed beneath side portions 266 for this alternative embodiment,planar center diffuser portion 268-10 may be positioned at the samehorizontal level as that of the adjacent side margins of side portions266.) The luminous intensity distribution of planar center diffuserportion 268-10 tracks approximately the luminous intensity distributionof light source 270. The tilt angles of side portions 266 range frombetween about 0 degrees and about ±30 degrees relative to horizontal.Two inwardly inclined white reflectors 268 r positioned on either sidemargin of center diffuser portion 268-10 close the open end spacesbetween side portions 266 and diffuser 268-10. (Reflectors 268 r wouldnot be used in the embodiment in which center diffuser portion 268-10and the adjacent side margins of side portions 266 are at the samehorizontal level.) Planar center diffuser portion 268-10 can be ofdissimilar type to that of side diffuser portion 266 and may include,for example, opal, sandblasted, or holographic diffusers, each of whicheither alone or in combination with perforated metal or paintedreflectors. Planar center diffuser portion 268-10 can be also formed ofperforated metal or opaque material.

FIGS. 32-6A and 32-6B show the batwing luminous intensity distributions,together with side elevation views of corresponding implementations, ofthe alternative embodiment of FIG. 32-4 at, respectively, smaller andlarger side panel tilt angles relative to horizontal.

In a fourteenth preferred embodiment (FIG. 33), a transparent substratecomposed of an annular generally planar section 278 and a generallycentrally located radially curved section 280 are positioned below apoint light source 282, with a circular distribution kinoform diffuser284 applied to the substrate on the side facing away from light source282. This embodiment creates a batwing luminous intensity distributionin a rotationally symmetric (i.e., circular) form directly below pointlight source 282. Because it contributes a generally lambertian luminousintensity distribution, curved section 280 can be replaced by a diffuserthat produces a similar luminous intensity distribution. Radially curvedsection 280 can be also formed of perforated metal or opaque material.Although a circular distribution kinoform diffuser 284 is preferred, acircular batwing luminous intensity distribution can be achieved withannular section 278 made of other diffuser material that results indiffused light at a range of exit angles that is narrower than a rangeof angles of incident light.

In a manner analogous to the embodiment of FIG. 32, in an alternativeembodiment, generally centrally located radially curved section 280 canbe replaced by a planar center diffuser portion similar to diffuserportion 268-10 of FIG. 32-5. The planar center diffuser portion tracksapproximately the luminous light intensity distribution of point lightsource 282. In this alternative embodiment, the diffuser 284 supportedon the annular substrate portion outside of curved section 280 and theplanar center diffuser portion cooperate to provide a batwing luminousintensity distribution pattern in a rotationally symmetric form. Theplanar center diffuser portion can be of dissimilar type to that ofdiffuser 284 supported on the annular substrate portion outside ofcurved section 280.

The advantages of the fourteenth preferred embodiment (FIG. 33) are thesame as those of the thirteenth preferred embodiment (FIG. 32).

In a fifteenth preferred embodiment (FIG. 34), a reflective kinoformdiffuser 290 with a linear or an elliptical distribution is positionedparallel to and above a major axis 288 of a linear light source 286.Diffuser 290 is oriented such that its plane of diffusion 292 isperpendicular to major axis 288 of light source 286. In accordance withthe novel retroreflective diffusion properties of reflective kinoformdiffusers as illustrated in FIG. 8F, a ray of incident light 294 emittedby light source 292 is diffused and preferentially redirected downwardsin the direction indicated by a set of rays 296.

The advantage of the fifteenth preferred embodiment is that it providesa controlled luminous intensity distribution that cannot be achievedwith conventional diffusers without the addition of lenses or curvedreflectors.

In a sixteenth preferred embodiment (FIG. 35), a reflective kinoformdiffuser 300 with a circular distribution is positioned above a pointlight source 298 or, in the alternative, parallel to and above the majoraxis of a linear light source. In accordance with the novelretroreflective diffusion properties of reflective kinoform diffusers asillustrated in FIG. 8F, a ray of incident light 302 emitted by lightsource 298 is diffused and preferentially redirected downwards in thedirection indicated by a set of rays 304.

The advantages of sixteenth preferred embodiment (FIG. 35) are the sameas those of the fifteenth preferred embodiment (FIG. 34).

In a seventeenth preferred embodiment (FIG. 36), a window or skylightcomposed of a transparent substrate 306 with a transmissive kinoformdiffuser 308 on the lower surface is illuminated by direct sunlight asthe sun 310 as it traverses the sky. In accordance with the noveldiffusion characteristics of transmissive kinoform diffusers asillustrated in FIG. 8F, incident rays 312 of direct sunlight arepreferentially diffused towards a diffuser surface normal or referencedirection 316, as indicated by sets of rays 314.

An advantage of the seventeenth preferred embodiment is that directsunlight is evenly diffused by kinoform diffuser 308. In accordance withthe elimination of the zero-order beam, diffuser 308 exhibits an evenluminance distribution across its surface. In particular, an image ofthe sun is not visible through diffuser 308, even as a blurred “hotspot.”

A second advantage of the seventeenth preferred embodiment is that thepreferential diffusion of the incident light 312 towards diffusersurface normal 316 improves the daylight utilization of the skylight orwindow, particularly when diffuser 308 is located at the top of a deepsky well. Skilled persons will appreciate that achieving suchredirection of incident light using conventional light control devicesrequires motor-driven mirrors and heliostats.

A third advantage of the seventeenth preferred embodiment is thatkinoform diffuser 308 may have a circular, elliptical, or lineardistribution, according to the need to distribute the diffused sunlightin an isotropic or anisotropic diffusion pattern.

It will be obvious to those having skill in the art that many changesmay be made to the details of the above-described preferred embodimentsof the invention without departing from the underlying principlesthereof. The scope of the present invention should, therefore, bedetermined only by the following claims.

I claim:
 1. A light control device implemented with a diffuserexhibiting a controllable luminous intensity distribution pattern inresponse to incident light, comprising: a substrate having first andsecond opposite major surfaces that receive incident light before andafter, respectively, wherein said incident light propagates within saidsubstrate; a generally centrally located region through which a firstportion of the incident light is transmitted; a diffuser supported onsaid second major surface and outside of said generally centrallylocated region, said diffuser being of a character that diffuses asecond portion of the incident light to form diffused light exhibiting adistribution pattern of luminous intensity, said diffuser and saidgenerally centrally located region having optical properties cooperatingsuch that said diffused light and said light transmitted through saidgenerally centrally located region exit said light control device in abatwing luminous intensity distribution pattern; wherein said diffuserincludes a microscopic surface relief pattern formed as one of saidmajor surfaces and further includes multiple light scattering elements,said light scattering elements producing diffused light in said batwingluminous intensity distribution pattern; said substrate including afirst and a second optically transparent portion separated by saidgenerally centrally located region, said diffuser including first andsecond diffuser portions; said incident light propagates from a lightsource, said first and second diffuser portions and said generallycentrally located region cooperate to provide said batwing luminousintensity distribution pattern; said first and second diffuser portionbeing positioned relative to said light source, said generally centrallylocated region positioned away from said light source, said generallycentrally located region including at least one central diffuser.
 2. Thelight control device of claim 1 wherein said at least one centraldiffuser is curved away from said light source.
 3. The light controldevice of claim 1 wherein said at least one central diffuser is flatplanar central diffuser.
 4. The light control device of claim 1 whereinsaid first and said second diffuser portions are angled away from saidlight source.
 5. The light control device of claim 1 wherein said firstand said second diffusers portions are angled towards said light source.6. The light control device of claim 1 wherein said generally centrallylocated region includes a first and a second central diffuser.
 7. Thelight control device of claim 1 wherein said central diffuser includes amicroscopic surface relief pattern formed as one of said major surfacesand further includes multiple light scattering elements, said lightscattering elements producing diffused light in said batwing luminousintensity distribution pattern.
 8. A light control device implementedwith a diffuser exhibiting a controllable luminous intensitydistribution pattern in response to incident light, comprising: asubstrate having first and second opposite major surfaces that receiveincident light before and after, wherein said incident light propagateswithin said substrate; said substrate including a first and a secondoptically transparent portion separated by a generally centrally locatedregion; said generally centrally located region through which a firstportion of the incident light is transmitted, said generally centrallylocated region including at least one central substrate; a diffuserincluding first and second diffuser portions supported on said secondmajor surface of said respective first and second optically transparentportions and outside of said generally centrally located region, saiddiffuser being of a character that diffuses a second portion of theincident light to form diffused light exhibiting a distribution patternof luminous intensity, said diffuser and said generally centrallylocated region having optical properties cooperating such that saiddiffused light and said light transmitted through said generallycentrally located region exit said light control device in a batwingluminous intensity distribution pattern; wherein said diffuser includesa microscopic surface relief pattern formed as one of said majorsurfaces and further includes multiple light scattering elements, saidlight scattering elements producing diffused light in said batwingluminous intensity distribution pattern; wherein said incident lightpropagates from a light source, said first and second diffuser portionsand said generally centrally located region cooperate to provide saidbatwing luminous intensity distribution pattern.
 9. The light controldevice of claim 8 wherein said at least one central substrate has atleast one central diffuser which includes a microscopic surface reliefpattern and further includes multiple light scattering elements, saidlight scattering elements producing diffused light in said batwingluminous intensity distribution pattern.
 10. The light control device ofclaim 9 wherein said at least one central diffuser includes a first anda second central diffuser angled away from said light sourcerespectively positioned on a first and a second central substrate. 11.The light control device of claim 10 wherein said at least one centraldiffuser further includes a microscopic surface relieve patternpositioned on a major surface of said substrate.
 12. The light controldevice of claim 11 wherein said major surface is an inner surfaceadjacent said light source.
 13. The light control device of claim 11wherein said major surface is an outer surface away from said lightsource.
 14. The light control device of claim 9 wherein said at leastone central substrate is a flat planar central substrate.
 15. The lightcontrol device of claim 9 wherein said at least one central substrate isa curved central substrate.
 16. A light control device implemented witha diffuser exhibiting a controllable luminous intensity distributionpattern in response to incident light, comprising: a light controlhousing supporting a first and second optically transparent substrate,said first and second optically transparent substrates separated by agenerally centrally located region; each of said first and secondoptically transparent substrates having first and second opposite majorsurfaces that receive incident light before and after, wherein saidincident light propagates through said substrate; a first portion ofsaid incident light transmitted through said generally centrally locatedregion, said generally centrally located region including at least onecentral substrate; a light source positioned within said light controlhousing and substantially above said at least one central substrate;first and second diffuser portions supported on one of said majorsurfaces of said respective first and second optically transparentsubstrates and outside of said generally centrally located region, saidfirst and second diffuser portions being of a character that diffuses asecond portion of the incident light to form diffused light exhibiting adistribution pattern of luminous intensity, said first and seconddiffuser portions and said generally centrally located region havingoptical properties cooperating such that said diffused light and saidlight transmitted through said generally centrally located region exitsaid light control device in a batwing luminous intensity distributionpattern; wherein said first and second diffuser portions include amicroscopic surface relief pattern formed as one of said major surfacesand further includes multiple light scattering elements, said lightscattering elements producing diffused light in said batwing luminousintensity distribution pattern; said incident light propagates from saidlight source, said first and second diffuser portions and said generallycentrally located region cooperate to provide said batwing luminousintensity distribution pattern.
 17. The light control device of claim 16wherein said at least one central substrate is a first and a secondcentral substrate angled away from said light source.
 18. The lightcontrol device of claim 16 wherein said at least one central substrateis a flat planar substrate positioned substantially below said lightsource.
 19. The light control device of claim 16 wherein said at leastone central substrate is curved away from said light source.
 20. Thelight control device of claim 16 wherein said at least one centralsubstrate includes a central diffuser, said central diffuser include amicroscopic surface relief pattern thereon and further includes multiplelight scattering elements, said light scattering elements producingdiffused light in said batwing luminous intensity distribution pattern.21. The light control device of claim 20 wherein said first and secondoptically transparent substrates are tilted at an angle with respect toa central axis of said light control housing.
 22. The light controldevice of claim 21 wherein said angle is an acute angle.
 23. The lightcontrol device of claim 21 wherein said angle is an obtuse angle.